Allodynia - pain due to a stimulus that does not normally provoke pain.

Analgesia - absence of pain in response to stimulation that would normally be painful.

Antibody - a special protein produced by the body's immune system that recognizes and helps fight infectious agents and other foreign substances that invade the body.

Arthralgia - pain in a joint, usually due to arthritis or arthropathy.

Arthritis - inflammation of a joint, usually accompanied by pain, swelling, and sometimes change in structure.

Arthroplasty - total joint replacement.

Arthroscopy - a minimally-invasive diagnostic and treatment procedure used for conditions of a joint. This procedure uses a small, lighted, optic tube (arthroscope) which is inserted into the joint through a small incision in the joint. Images of the inside of the joint are projected onto a screen; used to evaluate any degenerative and/or arthritic changes in the joint; to detect bone diseases and tumors; to determine the cause of bone pain and inflammation.

Cartilage - a type of tissue that covers the surface of a bone at a joint. Cartilage helps reduce the friction of movement within a joint.

Chondroblasts - immature cartilage-producing cells.

Compact tissue - the harder, outer tissue of bones.

Computed tomography scan (Also called CT or CAT scan.) - a diagnostic imaging procedure that uses a combination of x-rays and computer technology to produce horizontal, or axial, images (often called slices) of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, and organs. CT scans are more detailed than general x-rays.

Congenital - present at birth.

Contusion - a bruise caused by a blow to the muscle, tendon, or ligament; caused when blood pools around the injury and discolors the skin.

Corticosteroids - potent anti-inflammatory hormones that are made naturally in the body or synthetically for use as drugs; most commonly prescribed drug of this type is prednisone.

Immune system - complex network of specialized cells and organs that work together to defend the body against attacks by "foreign" invaders such as bacteria and viruses; in some rheumatic conditions, it appears that the immune system does not function properly and may even work against the body.

Incidence - statistic that equals the number of new cases of a particular disease that occur in a population during a defined period of time, usually one year.

Inflammation - a normal reaction to injury or disease, which results in swelling, pain, and stiffness.

Magnetic resonance imaging (MRI) - a diagnostic procedure that uses a combination of large magnets, radiofrequencies, and a computer to produce detailed images of organs and structures within the body.

Musculoskeletal system - the complex system involving the body's muscles and skeleton, and including the joints, ligaments, tendons, and nerves.

Myelogram - involves the injection of a dye or contrast material into the spinal canal; a specific x-ray study that also allows careful evaluation of the spinal canal and nerve roots.

Orthopedic surgeon (Also called an orthopedist.) - a physician who diagnoses, treats, manages the rehabilitation process, and provides prevention protocols for patients who suffer from injury or disease in any of the components of the musculoskeletal system.

Orthopedic surgery (Also called orthopedics.) - the medical specialty devoted to the diagnosis, treatment, rehabilitation, and prevention of injuries and diseases of the body's musculoskeletal system.

Osteoblast - cell found in bone; its function is to form the tissue that give bone its strength.

Osteoclast - very large cell formed in bone marrow; its function is to absorb and remove unwanted bone tissue.

Osteocyte - cell found within the bone; its function is to help maintain bone as living tissue.

Radionuclide bone scan - a nuclear imaging technique that uses a very small amount of radioactive material, which is injected into the patient's bloodstream to be detected by a scanner. This test shows blood flow to the bone and cell activity within the bone.

Radius - the shorter of the two long bones of the forearm.

Range of motion - measurement of the extent to which a joint can go through all its normal spectrum of movements.